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Home My WebLink About21770_Castle TIR_Approved Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 108 East 2nd Street, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net CITY OF RENTON TECHNICAL INFORMATION REPORT For Castle Development Townhouses 530 Shattuck Ave. South Renton, WA 98057 April 12, 2022 Revised June 8, 2022 Prepared By: Ian Dahl Encompass Engineering Job No. 21770 Prepared For: Yvonne Bui Castle Development LLC 6210 129th Place SE Bellevue, WA 98006 SURFACE WATER UTILITY jfarah 06/30/2022 DEVELOPMENT ENGINEERING YQI 07/06/2022 Castle Development Townhomes Technical Information Report 06/08/2022 Page i TABLE OF CONTENTS I. PROJECT OVERVIEW ................................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 6 III. OFFSITE ANALYSIS .................................................................................................................. 11 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ........................... 17 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 19 VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 19 VII. OTHER PERMITS ..................................................................................................................... 19 VIII. CSWPPP ANALYSIS AND DESIGN............................................................................................ 19 IX. BOND QUANTITIES AND DECLARATION OF COVENANT ....................................................... 22 X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 22 LIST OF FIGURES 1. TIR Worksheet 2. Vicinity Map 3. Soils Map and Legend 4. Existing Conditions Map 5. Developed Conditions Map 6. Drainage Review Flow Chart 7. Flow Control Applications Map 8. Aquifer Protection Zone Map 9. Downstream Map 10. Flow Frequency Return Periods LIST OF APPENDICES A. Geotechnical Report by Ages Engineering, Inc. dated April 11, 2022 B. WWHM2012 Output C. Operation & Maintenance Manual D. Declaration of Covenant CITY OF RENTON SURFACE WATER DESIGN MANUAL 2017 City of Renton Surface Water Design Manual 12/12/2016 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner _____________________________ Phone ___________________________________ Address __________________________________ _________________________________________ Project Engineer ___________________________ Company _________________________________ Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Land Use (e.g., Subdivision / Short Subd.)  Building (e.g., M/F / Commercial / SFR)  Grading  Right-of-Way Use  Other _______________________  DFW HPA  COE 404  DOE Dam Safety  FEMA Floodplain  COE Wetlands  Other ________  Shoreline Management  Structural Rockery/Vault/_____  ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final:  Full  Targeted  Simplified  Large Project  Directed ____________________________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final:  Full  Modified  Simplified ____________________________________ __________________ Yvonne Bui 206-280-2272 6210 129th Place SE Bellevue, WA 98006 Costa Philippides, PE Encompass Engineering & Surveying 425-392-0250 Castle Developments Townhouses 23 N 5 E SE 18 530 Shattuck Ave S TBD 04/12/2022 04/12/2022 06/08/2022 06/08/2022 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ Wellhead protection Area- Zone 2 Green River Valley Black River Peak Rate Flow Control Standard REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ On-site BMPs: _______________________________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Urban Land 0-2%Low Black River 1 12/6/2021 Limited Infiltration Gravel Trench, Permeable Pavement 1 TBD TBD TBD TBD X Seismic Hazard Area, Wellhead Protection Area- Zone 2 Peak Rate Flow Control REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): _______________ Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-Use Site: Yes / No Treatment BMP: _________________________________ Maintenance Agreement: Yes / No with whom? _____________________________________ Other Drainage Structures Describe: None Residential None 1 On-site roof drain system, conveyed to a private Type 1 Catch Basin which connects to the COR storm system off-site. REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-5 Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Control Pollutants  Protect Existing and Proposed BMPs/Facilities  Maintain Protective BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent BMPs/Facilities, restore operation of BMPs/Facilities as necessary  Flag limits of sensitive areas and open space preservation areas  Other _______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description  Detention  Infiltration  Regional Facility  Shared Facility  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ____________________________  Cast in Place Vault  Retaining Wall  Rockery > 4′ High  Structural on Steep Slope  Other _______________________________ Gravel Trench REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-6 Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date 06/08/2022 Castle Development Townhomes Technical Information Report 06/08/2022 Page 1 I. PROJECT OVERVIEW Project: Castle Development Townhouses Tax Parcel #: 784130-0400 Site Address: 530 Shattuck Ave. South Renton, WA 98057 Site Area: 9,602 SF (0.220 AC) – As Surveyed Zoning: R-14 Legal Description: LOTS 5 AND 6, BLOCK 5, SMITHERS FIFTH ADDITION TO THE TOWN OF RENTON, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 16 OF PLATS, PAGE 33, RECORDS OF KING COUNTY, WASHINGTON. Figure 2: Vicinity Map Existing Site Conditions: The project is located in the City of Renton on a 9,602 SF (0.220 AC) parcel zoned R-14. The site is currently developed with two concrete building pads and various sewer, water and storm utility stubs from the abandoned Allen Kim Townhouses project. Slopes on-site range from 0-2% towards the project frontage on Shattuck Ave S to the west. The project is bordered by single family residences to the north and south, Shattuck Ave S to the west and an unnamed alley to the east. Runoff leaves the site through one Natural Discharge Area (NDA) at the western limit of the site creating a single Threshold Discharge Area (TDA) for the project. See Section III of this report for a full Offsite Analysis and Figure 4 for a map of the existing site conditions. Castle Development Townhomes Technical Information Report 06/08/2022 Page 2 Critical Areas: Encompass has reviewed the site and the applicable resources for both listed and potential problems. The project site falls within a Seismic Hazard Area, as well as a Wellhead Protection Area- Zone 2 per the City of Renton maps. No other critical areas were identified per FEMA maps, King County Sensitive Areas Folio, CED Wetlands Inventory, or the Washington State DOE Section 303d list. Soils: Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey information, the project site is generally underlain with Urban Land (Ur). Per the Geotechnical Report prepared by Ages Engineering, the site is underlain with 3 feet of fill soils overlying silty sand to sand with silt consistent with Alluvium. Limited Infiltration is feasible in these soils. The full Geotechnical Report is included in Appendix A of this report. Figure 3: Soils Map and Legend SHATTUCK AVE S. ALLEY IN COMPLIANCE WITH CITY OF RENTON STANDARDSKnow what'sCallbelow.before you dig.REastern Washington Division407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433Western Washington Division165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250TED-40-4215 PR22-000064 C22000675 SW 1/4 OF SE 1/4 OF SECTION 18, T. 23 N., R. 05 E., W.M.CITY OF RENTON, STATE OF WASHINGTONCASTLE DEVELOPMENT TOWNHOMESCASTLE DEVELOPMENT TOWNHOMESFIGURE 4- EXISTING CONDITIONS MAPCASTLE DEVELOPMENT TOWNHOMES---- CASTLE DEVELOPMENT TOWNHOMES NORTH EXISTING CONDITIONS AREAS PREDEVELOPED MODELED AREAS Castle Development Townhomes Technical Information Report 06/08/2022 Page 4 Developed Site Conditions: This proposal incorporates the demolition, clearing and grading required to accommodate the construction of a 3-plex townhouse with two detached garage structures providing driveway access to the alley on the eastern limit of the site. Proposed impervious surfaces include 4,586 SF of rooftop, 594 SF of driveway, and 850 SF of walkways and patios. The total proposed on-site impervious surface is 6,010 SF. Additionally, 683 SF of sidewalk is proposed in the ROW. Water services will be provided from Shattuck Ave S, and sewer services will be provided from the Alley to the east of the site. Limited infiltration is feasible on this site, and is proposed for all garage rooftop areas in the eastern portion of the site. The remainder of runoff from target impervious areas will be tightlined to a private catch basin on the western side of the site, before discharging to an existing catch basin on the east side of Shattuck Ave S. Additionally, walkway and driveway areas on the site will be paved with permeable pavement. See Section IV of this report for a full discussion of the proposed stormwater controls and Figure 5 for a map of the developed site conditions. SHATTUCK AVE S. ALLEY SHATTUCK AVE S. ALLEYUNIT AUNIT BUNIT CUNIT C GARAGEUNIT B GARAGEUNIT A GARAGEIN COMPLIANCE WITH CITY OF RENTON STANDARDSKnow what'sCallbelow.before you dig.REastern Washington Division407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433Western Washington Division165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250TED-40-4215 PR22-000064 C22000675 SW 1/4 OF SE 1/4 OF SECTION 18, T. 23 N., R. 05 E., W.M.CITY OF RENTON, STATE OF WASHINGTONCASTLE DEVELOPMENT TOWNHOMESCASTLE DEVELOPMENT TOWNHOMESFIGURE 5- DEVELOPED CONDITIONS MAPCASTLE DEVELOPMENT TOWNHOMES---- CASTLE DEVELOPMENT TOWNHOMES NORTH DEVELOPED CONDITIONS AREAS MITIGATED MODELED AREAS Castle Development Townhomes Technical Information Report 06/08/2022 Page 6 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2017 City of Renton Surface Water Design Manual (RSWDM) has been utilized for stormwater design per the City of Renton requirements. The development will result in over 2,000 SF of new plus replaced impervious surface but does not result in over 50 acres of new impervious surface within a subbasin or multiple subbasins that are hydraulically connected. Therefore, per Figure 1.1.2.A of the RSWDM, this project must meet the Full Drainage Review requirements as detailed in Section 1.1.2.4. See Figure 6 below for more information on how the type of drainage review was determined. Figure 6: Drainage Review Flow Chart Castle Development Townhomes Technical Information Report 06/08/2022 Page 7 Core Requirements: Core Requirement #1: Discharge at the Natural Location Currently, runoff from the site follows gentle slopes to the west towards the public storm system on Shattuck Ave S. In addition, two existing on-site catch basins from the abandoned Allen Kim Townhouses project connect to the adjacent Type 1 CB in the Shattuck Ave S ROW just west of the site via a 12” pipe. This project proposes to preserve the existing site drainage patterns via an on-site storm system which will tightline runoff from target impervious areas to the existing off- site catch basin on Shattuck Ave S. Core Requirement #2: Offsite Analysis A Level 1 Downstream analysis has been prepared and is included in Section III of this TIR. Core Requirement #3: Flow Control Facilities Per the City of Renton Flow Control Application Map (Figure 7), this project site is located within the “Peak Rate Flow Control Standard (Existing Site Conditions)” area. In this area, flow control facilities are required to be designed to match the existing conditions 2-, 10- and 100-year peak- rate runoff from the site. The on-site BMPs for this project have been designed for the final developed impervious surface areas. After applying the modeling credits per Table 1.2.9.A of the RSWDM for the on-site BMPs listed in Core Requirement #9, the WWHM output displayed an increase in the 100-year peak flow runoff of 0.0075 CFS using 15-minute timesteps. Therefore, the project meets the exemption for Peak Rate Flow Control Standard Areas per Section 1.2.3.1 of the RSWDM. See Section IV for further discussion and Appendix B for the full WWHM2012 Output. Figure 7: Flow Control Application Map Castle Development Townhomes Technical Information Report 06/08/2022 Page 8 Core Requirement #4: Conveyance System The conveyance capacity of the 8” SD pipe from the on-site catch basin to the exiting catch basin in Shattuck Ave S. has been calculated to confirm it will not be exceeded. See Section V of this TIR for further detail. Core Requirement #5: Construction Stormwater Pollution Prevention A simplified Construction Stormwater Pollution Prevention Plan (CSWPPP) is included in section VIII of this report. In addition, a corresponding Temporary Erosion and Sediment Control (TESC) Plan is included in the civil plans. Core Requirement #6: Maintenance and Operations See Section X of this report for a full discussion of the maintenance and operations. Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Core Requirement #8: Water Quality Facilities In accordance with Section 1.2.8 of the RSWDM, Water Quality Treatment is not required for this project as new plus replaced pollution generating impervious surfaces (PGIS) do not exceed 5,000 SF, meeting exemption 1. Only 594 SF of asphalt driveway is proposed on the eastern portion of the site, connecting to the alley. Core Requirement #9: On-Site BMPs per Section 1.2.9.1 of the 2017 Renton SWDM This project is smaller than 22,000 SF, and has therefore been designed to comply with the Small Lot BMP Requirements detailed in Section 1.2.9.2.1 of the RSWDM. On-site BMPs detailed below have been evaluated in order of preference per Section 1.2.9.2.1. The On-site BMPs for this project have been designed per the final developed impervious surface areas. See Section IV of this report for further discussion. Impervious Surface BMPs Full Dispersion: Infeasible. The site does not allow for the minimum 100-foot native vegetated flowpath lengths required per Appendix C.2.1 of the RSWDM. Full Infiltration: Infeasible. On-site soils have the capacity to infiltrate per the Geotechnical Report by Ages Engineering, Inc.; however, the soils have been classified as loamy sand which only meet the criteria for limited infiltration. Limited Infiltration: Feasible. Per the Preliminary Geotechnical Report by Ages Engineering, Inc., soils on-site are suitable for limited infiltration with the classification of loamy sand. For rainfall regions greater than SeaTac 1.0, a 2-foot wide gravel trench must be 48.3 feet in length in loamy sand soils to mitigate 1,000 SF of impervious surface. Due to setback requirements of 5 feet from structures and property lines, as well as utility conflicts, the only feasible location for a gravel filled infiltration trench is in the eastern portion of the site. A 6’x20’ gravel filled trench has been designed to mitigate runoff from the 1,110 SF Unit B & C garage rooftop area. A 48.3-foot by 2-foot trench has a surface area of 96.6 SF; therefore, 96.6 SF of gravel infiltration trench can infiltrate up to 1,000 SF of impervious area. A Castle Development Townhomes Technical Information Report 06/08/2022 Page 9 6’x20’ trench has 120 SF of surface area and therefore can infiltrate up to (120/96.6)x 1,000=1,242 SF of impervious area. This is larger than the 1,110 SF of tributary rooftop area. An overflow will be provided, connecting to the private stormwater catch basin on the west side of the site, before leaving the site and entering the City of Renton storm system. Additionally, a 5’x 12’ trench has been sized for the 575 SF rooftop area of Garage A, which can infiltrate up to (60/96.6)x 1,000=600 SF of impervious area. This trench is also have overflow system connected the private catch basin on the west side of the site. Rain Gardens/Bioretention: Infeasible. The site layout does not allow for the implementation of rain gardens or bioretention facilities with setbacks from structures and property lines. Permeable Pavement: All on-site walkways and driveways will be constructed of materials meeting the requirements for permeable pavement per Section C.2.7 of the RSWDM. The project will utilize either porous pavement or permeable pavers for the approximately 850 SF of on-site walkways and 594 SF of driveways. Basic Dispersion: Infeasible. The site plan does not allow for the required dispersion flowpaths over vegetated surfaces per Appendix C.2.4 of the RSWDM. BMPs Must be implemented, at minimum, for an impervious area equal to at least 10% of the site/lot for site/lot sizes up to 11,000 SF. This project site is 9,602 SF; therefore, 960 SF of impervious area must mitigated by BMPs. Permeable pavement is proposed for on-site walkway and driveways areas as well as garage roof areas, totaling 3,129 SF, meeting this minimum requirement. Perforated Pipe Connection: All Proposed roof downspout connections to the local drainage system will use perforated pipe connections per Section 1.2.9.2.1 of the 2017 RSWDM. 10 feet of perforated pipe trench is required for every 5,000 SF of impervious surface. As 4,586 SF of roof area is proposed, two 10-foot trenches located on the eastern side of the site will meet this requirement. Pervious Surface BMPs Soil Amendment: Feasible for new pervious surfaces Retention of the existing soils and restoration of all disturbed soils shall be applied to all of the landscaped areas both on- and off-site per Appendix C.2.13 of the RSWDM. Castle Development Townhomes Technical Information Report 06/08/2022 Page 10 Special Requirements: Special Requirement #1: Other Adopted Area-Specific Requirements Master Drainage Plan – N/A Basin Plan – N/A Salmon Conservation Plan – N/A Lake Management Plan – Lake Washington Management Plan Hazard Mitigation Plan – N/A Shared Facility Drainage Plan – N/A Special Requirement #2: Flood Hazard Area Delineation The limits of this project do not lie in the FEMA 100-year floodplain. Special Requirement #3: Flood Protection Facilities This special requirement is applicable for Class 1 or 2 streams with an existing flood protection facility. The site does not contain any streams. Therefore, Special Requirement #3 is not applicable to this project. Special Requirement #4: Source controls Source control is not required for this project. Special Requirement #5: Oil Control This project is not considered high-use in need of oil control. Special Requirement #6: Aquifer Protection Area Per COR Maps, the project is located within an Aquifer Protection Area Zone 2. Castle Development Townhomes Technical Information Report 06/08/2022 Page 11 III. OFFSITE ANALYSIS Task 1: Study Area Definition and Maps A Level 1 Offsite Analysis has been performed for the project site per Section 2.3.1.1 of the RSWDM. The site is located in the Black River Drainage Basin, within the Duwamish- Green River Watershed. Existing structures on the site consist of two concrete building pads and various utility stubs for storm, sewer and water from the abandoned Allen Kim Townhomes project. The remainder of the site is grass lawn area. No paved driveways currently access the site from Shattuck Ave S to the west or the alley to the east. Slopes range from 0-1% across the site, sloping towards the west. The study area for this analysis extends downstream of the project site for approximately one quarter mile and includes no upstream offsite drainage area tributary to the project site. Stormwater leaves the site in one NDA, creating a single TDA for the project. A map showing the study area is included in Figure 9. Task 2: Resource Review Encompass has reviewed the site and the applicable resources for both listed and potential problems. The project site falls within a Seismic Hazard Area, as well as a Wellhead Protection Area- Zone 2 per the City of Renton maps. No other critical areas were identified per FEMA maps, King County Sensitive Areas Folio, CED Wetlands Inventory, or the Washington State DOE Section 303d list. Task 3: Field Inspection A Level 1 Downstream Analysis was performed by Encompass Engineering and Surveying on Monday, December 6, 2021. The analysis was performed at approximately 2:00 PM with a temperature of about 45°. Information collected during this study is included in the Task 4 system description. Task 4: Drainage System Description and Problem Descriptions Stormwater sheet flows to the west towards Shattuck Ave S or is collected in two on-site catch basins from an abandoned development and conveyed to an existing Type 1 CB (Element 1) on the east side of the road. Stormwater is then conveyed across the road to the west via a 12-inch polyethylene pipe to a Type 2 CB (Element 2). From here, stormwater is conveyed to the south via a 48” polyethylene pipe along the west side of the road and passes through two additional Type 2 CBs (Elements 3 & 4) at the intersection of S 6th St and Shattuck Ave S. Stormwater continues to the south and passes through another Type 2 CB (Element 5) along the west side of Shattuck Ave S, before entering a Type 2 CB (Element 6) just north of the intersection of S 7th St and Shattuck Ave S. At the intersection of S 7th St and Shattuck Ave S stormwater enters an underground vault (Element 7) per COR Maps. Stormwater then is conveyed to the west along the north side of S 7th St via a 24” poly pipe. Stormwater enters a Type 1 CB (Element 8), and continues west via 12” concrete pipe through four Type 2 CBs (Elements 9, 10, 11 & 12) before entering the intersection of S 7th St and Rainier Ave S at ¼ mile downstream of the site. This is where the downstream analysis was concluded. No existing or potential drainage problems were identified. Castle Development Townhomes Technical Information Report 06/08/2022 Page 12 Figure 9: Downstream Map Castle Development Townhomes Technical Information Report 06/08/2022 Page 13 OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE BASIN: Black River SUBBASIN NAME: SUBBASIN NUMBER: SYMBOL DRAINAGE COMPONENT TYPE, NAME, AND SIZE DRAINAGE COMPONENT DESCRIPTION SLOPE DISTANCE FROM SITE DISCHARGE EXISTING PROBLEMS POTENTIAL PROBLEMS OBSERVATIONS OF FIELD INSPECTOR, RESOURCE REVIEWER, OR RESIDENT (See map) Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area Drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 Mile = 1,320 ft Constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion Tributary area, likelihood of problem, overflow pathways, potential impacts 1 CATCH BASN TYPE 1 N/A 10’ NONE NONE CONNECTION TO ON-SITE CATCH BASINS 2 CATCH BASIN TYPE 2 N/A 45’ NONE NONE 12” POLY PIPE 3 CATCH BASIN TYPE 2 N/A 225' NONE NONE 48” POLY PIPE 4 CATCH BASIN TYPE 2 N/A 240’ NONE NONE 48” POLY PIPE 5 CATCH BASIN TYPE 2 N/A 480' NONE NONE 48” POLY PIPE 6 CATCH BASIN TYPE 2 N/A 665’ NONE NONE 48” POLY PIPE 7 STORM VAULT 8’X18’ N/A 700' NONE NONE 48” POLY PIPE 8 CATCH BASIN TYPE 1 N/A 840' NONE NONE 24” POLY PIPE 9 CATCH BASIN TYPE 2 N/A 890' NONE NONE 24” CONCRETE PIPE 10 CATCH BASIN TYPE 2 N/A 1070' NONE NONE 24” CONCRETE PIPE 11 CATCH BASIN TYPE 2 N/A 1160’ NONE NONE 24” CONCRETE PIPE 12 CATCH BASIN TYPE 2 N/A 1260’ NONE NONE 24” CONCRETE PIPE 13 CATCH BASIN TYPE 2 N/A 1370’ NONE NONE 24” CONCRETE PIPE Table 1: Downstream Table Castle Development Townhomes Technical Information Report 06/08/2022 Page 14 Element 1: Type 1 CB at project frontage on Shattuck Ave S Element 2: Type 2 CB on Shattuck Ave S Castle Development Townhomes Technical Information Report 06/08/2022 Page 15 Elements 3 & 4: Type 2 CBs Element 6: Type 2 CB at intersection of Shattuck Ave S and S 7th St Castle Development Townhomes Technical Information Report 06/08/2022 Page 16 Element 12: Type 2 CB at intersection of S 7th St and Rainier Ave S Task 5: Mitigation of Existing or Potential Problems Both King County iMap and the City of Renton GIS Maps show no drainage complaints relevant to the project or the downstream drainage paths within the study limits. No existing or potential problems were observed within the site or downstream area during the field reconnaissance. Castle Development Townhomes Technical Information Report 06/08/2022 Page 17 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The site is located in the Black River Drainage Basin, within the Duwamish-Green River Watershed. Existing structures on the site consist of two concrete building pads and various utility stubs for storm, sewer and water from the abandoned Allen Kim Townhouses Development. The remainder of the site is grass lawn area which slopes towards the west at 0-2%. Stormwater leaves the site via sheet flow towards Shattuck Ave S or is conveyed towards an existing off-site Type 1 CB on Shattuck Ave S from two on-site catch basins. Stormwater leaves the site in one NDA, creating a single TDA for the project. Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey information, the project site is generally underlain with Urban Land (Ur). Per the Geotechnical Report prepared by Ages Engineering, the site is underlain with 3 feet of fill soils overlying silty sand to sand with silt consistent with Alluvium. Limited Infiltration is feasible in these soils. The full Geotechnical Report is included in Appendix A of this report. Per Core Requirement #3, the pre-developed site has been modeled as “Existing Conditions” for the purposes of stormwater calculations. Table 2 below shows a breakdown of the measured and modeled acreages for the existing conditions. See Figure 4 for a map of the existing site conditions and Appendix B for the full stormwater modeling calculations. Existing Conditions Areas Measured Modeled Condition Area (AC) Area (AC) Lawn: 0.14 0.14 Concrete Slab: 0.08 0.08 Total Area: 0.22 0.22 Table 2: Existing Conditions Model Part B: Developed Site Hydrology This proposal incorporates the demolition, clearing and grading required to accommodate the construction of a 3-plex townhouse with two detached garage structures providing driveway access to the alley on the eastern limit of the site. Proposed impervious surfaces include 4,586 SF of rooftop, 594 SF of driveway, and 850 SF of walkways and patios. The total proposed on-site impervious surface is 6,010 SF. Additionally, 683 SF of sidewalk is proposed in the ROW. On-site walkways and driveways will be constructed to meet the requirements of Permeable Pavement per Appendix C.2.7 of the RSWDM. Modeling credit has been applied to impervious surfaces utilizing BMPs per Table 1.2.9.A of the RSWDM. In addition, the Soil Amendment BMP shall be implemented for all on- and off-site vegetated areas per Appendix C.2.13 of the RSWDM. Areas meeting this criterion have been modeled as “pasture” rather than “lawn” in WWHM. Finally, roof drains connection to the COR storm system will utilize perforated pipe connections per Section 1.2.9.2.1 of the 2017 Renton SWDM. See Table 3 for a breakdown of the measured and modeled acreages for the developed conditions, Figure 5 for the developed site conditions, and Appendix B for the full stormwater modeling calculations. Castle Development Townhomes Technical Information Report 06/08/2022 Page 18 Developed Conditions Areas Measured Modeled Condition Area (AC) Area (AC) Pasture: 0.00 0.07 Lawn: 0.07 0.01 Roof: 0.10 0.10 Walkway/Patio: 0.04 0.03 Driveway: 0.01 0.01 Total Area: 0.22 0.22 Table 3: Developed Conditions Model Part C: Performance Standards This project site is located within the “Peak Rate Flow Control Standard (Existing Site Conditions)” area. In this area, flow control facilities are required to be designed to match the existing conditions 2-, 10- and 100-year peak-rate runoff from the site. In addition, this site has been designed to comply with the Small Lot BMP Requirements detailed in Section 1.2.9.3.1 of the RSWDM. On-site BMPs per Section 1.2.9.1 of the 2017 RSWDM have been considered in order of preference as prescribed by the Small Lot BMP Requirements and are detailed in Core Requirement #9 in Section II of this report. This project proposes the creation of less than 5,000 SF of new PGIS; therefore, this project meets Exemption 1 and water quality treatment is not required per Section 1.2.8.1 of the RSWDM. Part D: Flow Control System After applying the modeling credits per Table 1.2.9.A of the RSWDM for the on-site BMPs listed in Core Requirement #9, the WWHM output displayed an increase in the 100-year peak flow runoff of 0.0075 CFS using 15-minute timesteps. Therefore, the project meets the exemption for Peak Rate Flow Control Standards per Section 1.2.3.1 of the RSWDM, which states that the flow control requirement is waived for a project that results in less than a 0.15 CFS increase in the 100-year peak flow. The summary output table from WWHM is provided as Figure 10 below, and the full WWHM output is provided in Appendix B. No additional flow control facilities are required at this time. Figure 10: Flow Frequency Return Periods Part E: Water Quality System In accordance with Section 1.2.8 of the RSWDM, Water Quality Treatment is not required for this project as new plus replaced pollution generating impervious surfaces (PGIS) do not exceed 5,000 SF, meeting exemption 1. Only 594 SF of asphalt driveway is proposed on the eastern portion of the site, connecting to the alley. Castle Development Townhomes Technical Information Report 06/08/2022 Page 19 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN The conveyance capacity of the 8” SD pipe from the on-site catch basin to the exiting catch basin in Shattuck Ave S. was calculated using a Manning’s Equation calculator. An 8” pipe at 0.5% slope can convey 1.08 cfs (See below). The 25-year storm in the developed condition generates 0.0941 cfs of runoff. This does not exceed the capacity of the proposed pipe. VI. SPECIAL REPORTS AND STUDIES Geotechnical Report prepared by Ages Engineering, dated April 11, 2022. VII. OTHER PERMITS A Building Permit, R.O.W. Permit, and a Clearing and Grading Permit will be required. VIII. CSWPPP ANALYSIS AND DESIGN 1. Preserve Vegetation/Mark Clearing Limits a. The clearing limits are shown on the TESC plans surrounding all proposed construction activity. High visibility orange fencing is shown around the perimeter of the site. b. Retain the duff layer, native top soil and natural vegetation in an undisturbed state to the maximum degree practicable. 2. Establish Construction Access a. A stabilized construction entrance is shown for the project off of the alley east of the project site. b. If sediment is tracked off site, the affected roadways are to be cleaned thoroughly at the end of each day. 3. Control Sediment a. Silt fence will also be utilized to control sediment and protect adjacent properties. 4. Install Sediment Controls a. Silt fence will be installed around the perimeter of the site during the initial phase of construction. 5. Stabilize Soils a. Stabilize expose and unworked soils. Soils must not remain exposed and unworked for more than the time periods set forth below to prevent erosion: Castle Development Townhomes Technical Information Report 06/08/2022 Page 20 • During the dry season (May 1 – September 30): 7 days • During the wet season (October 1 – April 30): 2 days • Stabilize soils at the end of the shift before a holiday or weekend if needed based on the weather forecast. b. Stockpiled soils to be covered with plastic. c. All disturbed areas shall be stabilized with landscaping or some other method prior to final construction approval. 6. Protect Slopes a. Design and construct cut-and-fill slopes in a manner to minimize erosion. 7. Protect Drain Inlets a. Drain inlets on the site and on Shattuck Ave S will equipped with inlet protection devices in the initial stages of construction. b. Clean or remove and replace inlet protection devices when sediment has filled one third of the available storage. 8. Stabilize Channels and Outlets a. No channels or outlets are proposed. 9. Control Pollutants a. Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants. b. Handle and dispose all pollutants, including waste materials and demolition debris that occur on-site in a manner that does not cause contamination of stormwater. c. Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks must include secondary containment. Secondary containment means placing tanks or containers within an impervious structure capable of containing 110% of the volume contained in the largest tank within the containment structure. Double-walled tanks do not require additional secondary containment. d. Conduct maintenance, fueling and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident. e. Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that prevents discharge to surface water, such as closed-loop recirculation or upland application, or to the sanitary sewer, with local sewer district approval. f. Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Follow manufacturers’ label requirements for application rates and procedures. g. Use BMPs to prevent contamination of stormwater runoff by pH modifying sources. The sources for this contamination include, but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. h. Adjust the pH of stormwater if necessary to prevent violations of water quality standards. i. Assure that washout of concrete trucks is performed off-site or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. Do not dump excess concrete on-site, except in designated concrete washout areas. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Castle Development Townhomes Technical Information Report 06/08/2022 Page 21 j. Obtain written approval from Ecology before using chemical treatment other than CO2 or dry ice to adjust pH. 10. Control Dewatering a. Dewatering is not anticipated at this site. 11. Maintain BMPs a. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. b. Remove all temporary erosion and sediment control BMPs within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. All disturbed areas shall be stabilized with landscaping or some other method prior to final construction approval. 12. Manage the Project a. Maintain an updated SWPPP 13. Protect Low Impact Development BMPs. a. Porous pavement used in walkways and driveway areas will be poured after site is stabilized. Any excess debris or sediment tracked onto the pavement will be washed and/or vacuumed. Follow operation and maintenance procedures laid out in Appendix C. b. Perforated pipe connections will be covered with filter fabric immediately after pipe is backfilled with washed rock to prevent sediment from entering the system. Castle Development Townhomes Technical Information Report 06/08/2022 Page 22 IX. BOND QUANTITIES AND DECLARATION OF COVENANT A Declaration of Covenant for stormwater BMPs is provided in Appendix D. A Bond Quantities Worksheet has been provided in a separate document. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual has been prepared for the site and is included in Appendix C of this Report. Appendix A Geotechnical Report prepared by Ages Engineering dated April 11, 2022 Appendix B WWHM2012 Output WWHM2012 PROJECT REPORT 21770 WWHM 2/14/2022 4:52:57 PM Page 2 General Model Information Project Name:21770 WWHM Site Name: Site Address: City: Report Date:2/14/2022 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2021/08/18 Version:4.2.18 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 21770 WWHM 2/14/2022 4:52:57 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Flat 0.14 Pervious Total 0.14 Impervious Land Use acre SIDEWALKS FLAT 0.08 Impervious Total 0.08 Basin Total 0.22 Element Flows To: Surface Interflow Groundwater 21770 WWHM 2/14/2022 4:52:57 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Pasture, Flat 0.07 C, Lawn, Flat 0.01 Pervious Total 0.08 Impervious Land Use acre ROOF TOPS FLAT 0.1 DRIVEWAYS FLAT 0.01 SIDEWALKS FLAT 0.03 Impervious Total 0.14 Basin Total 0.22 Element Flows To: Surface Interflow Groundwater 21770 WWHM 2/14/2022 4:52:57 PM Page 5 Routing Elements Predeveloped Routing 21770 WWHM 2/14/2022 4:52:57 PM Page 6 Mitigated Routing 21770 WWHM 2/14/2022 4:52:57 PM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.14 Total Impervious Area:0.08 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.08 Total Impervious Area:0.14 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.040183 5 year 0.055545 10 year 0.066731 25 year 0.082054 50 year 0.094356 100 year 0.107438 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.055371 5 year 0.070414 10 year 0.080688 25 year 0.09407 50 year 0.104348 100 year 0.114906 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.060 0.074 1950 0.059 0.075 1951 0.037 0.047 1952 0.024 0.039 1953 0.025 0.042 1954 0.032 0.045 1955 0.035 0.051 1956 0.035 0.050 1957 0.045 0.058 1958 0.030 0.046 21770 WWHM 2/14/2022 4:53:32 PM Page 8 1959 0.026 0.045 1960 0.039 0.049 1961 0.037 0.049 1962 0.026 0.041 1963 0.035 0.048 1964 0.032 0.045 1965 0.048 0.059 1966 0.027 0.040 1967 0.059 0.066 1968 0.055 0.075 1969 0.043 0.054 1970 0.037 0.052 1971 0.044 0.061 1972 0.057 0.066 1973 0.023 0.037 1974 0.043 0.056 1975 0.046 0.062 1976 0.033 0.045 1977 0.031 0.045 1978 0.038 0.056 1979 0.046 0.076 1980 0.067 0.074 1981 0.040 0.058 1982 0.068 0.082 1983 0.042 0.064 1984 0.030 0.042 1985 0.041 0.056 1986 0.037 0.049 1987 0.047 0.075 1988 0.026 0.045 1989 0.032 0.056 1990 0.107 0.111 1991 0.076 0.083 1992 0.029 0.042 1993 0.023 0.035 1994 0.022 0.038 1995 0.035 0.051 1996 0.049 0.058 1997 0.043 0.055 1998 0.034 0.052 1999 0.088 0.108 2000 0.040 0.055 2001 0.036 0.058 2002 0.060 0.072 2003 0.046 0.058 2004 0.081 0.103 2005 0.037 0.049 2006 0.035 0.043 2007 0.097 0.097 2008 0.075 0.082 2009 0.046 0.069 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1070 0.1111 2 0.0970 0.1082 3 0.0884 0.1027 21770 WWHM 2/14/2022 4:53:32 PM Page 9 4 0.0806 0.0975 5 0.0763 0.0833 6 0.0748 0.0819 7 0.0675 0.0816 8 0.0670 0.0762 9 0.0598 0.0751 10 0.0597 0.0750 11 0.0592 0.0748 12 0.0586 0.0739 13 0.0574 0.0738 14 0.0545 0.0716 15 0.0491 0.0690 16 0.0476 0.0664 17 0.0470 0.0657 18 0.0464 0.0644 19 0.0460 0.0624 20 0.0459 0.0614 21 0.0459 0.0594 22 0.0448 0.0583 23 0.0444 0.0582 24 0.0434 0.0577 25 0.0430 0.0576 26 0.0428 0.0575 27 0.0416 0.0565 28 0.0405 0.0565 29 0.0404 0.0564 30 0.0399 0.0556 31 0.0389 0.0550 32 0.0382 0.0550 33 0.0374 0.0536 34 0.0371 0.0524 35 0.0369 0.0520 36 0.0369 0.0508 37 0.0366 0.0506 38 0.0358 0.0498 39 0.0355 0.0494 40 0.0349 0.0493 41 0.0346 0.0487 42 0.0346 0.0487 43 0.0346 0.0477 44 0.0342 0.0471 45 0.0334 0.0456 46 0.0323 0.0454 47 0.0323 0.0454 48 0.0318 0.0453 49 0.0313 0.0452 50 0.0303 0.0448 51 0.0297 0.0447 52 0.0294 0.0434 53 0.0266 0.0418 54 0.0263 0.0416 55 0.0259 0.0416 56 0.0258 0.0414 57 0.0255 0.0395 58 0.0243 0.0386 59 0.0232 0.0377 60 0.0228 0.0371 61 0.0215 0.0352 Appendix C Operation & Maintenance Manual APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-4 NO. 2 – INFILTRATION FACILITIES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Site Trash and debris Any trash and debris which exceed 1 cubic foot per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Trash and debris cleared from site. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to City personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where City personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Excessive growth of grass/groundcover Grass or groundcover exceeds 18 inches in height. Grass or groundcover mowed to a height no greater than 6 inches. Infiltration Pond, Top or Side Slopes of Dam, Berm or Embankment Rodent holes Any evidence of rodent holes if facility is acting as a dam or berm, or any evidence of water piping through dam or berm via rodent holes. Rodents removed or destroyed and dam or berm repaired. Tree growth Tree growth threatens integrity of dams, berms or slopes, does not allow maintenance access, or interferes with maintenance activity. If trees are not a threat to dam, berm, or embankment integrity or not interfering with access or maintenance, they do not need to be removed. Trees do not hinder facility performance or maintenance activities. Erosion Eroded damage over 2 inches deep where cause of damage is still present or where there is potential for continued erosion. Any erosion observed on a compacted slope. Slopes stabilized using appropriate erosion control measures. If erosion is occurring on compacted slope, a licensed civil engineer should be consulted to resolve source of erosion. Settlement Any part of a dam, berm or embankment that has settled 4 inches lower than the design elevation. Top or side slope restored to design dimensions. If settlement is significant, a licensed civil engineer should be consulted to determine the cause of the settlement. Infiltration Pond, Tank, Vault, Trench, or Small Basin Storage Area Sediment accumulation If two inches or more sediment is present or a percolation test indicates facility is working at or less than 90% of design. Facility infiltrates as designed. Liner damaged (If applicable) Liner is visible or pond does not hold water as designed. Liner repaired or replaced. Infiltration Tank Structure Plugged air vent Any blockage of the vent. Tank or vault freely vents. Tank bent out of shape Any part of tank/pipe is bent out of shape more than 10% of its design shape. Tank repaired or replaced to design. Gaps between sections, damaged joints or cracks or tears in wall A gap wider than ½-inch at the joint of any tank sections or any evidence of soil particles entering the tank at a joint or through a wall. No water or soil entering tank through joints or walls. Infiltration Vault Structure Damage to wall, frame, bottom, and/or top slab Cracks wider than ½-inch, any evidence of soil entering the structure through cracks or qualified inspection personnel determines that the vault is not structurally sound. Vault is sealed and structurally sound. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-5 NO. 2 – INFILTRATION FACILITIES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Inlet/Outlet Pipes Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. Damaged inlet/outlet pipe Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Access Manhole Cover/lid not in place Cover/lid is missing or only partially in place. Any open manhole requires immediate maintenance. Manhole access covered. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs of lift. Cover/lid can be removed and reinstalled by one maintenance person. Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards. Allows maintenance person safe access. Large access doors/plate Damaged or difficult to open Large access doors or plates cannot be opened/removed using normal equipment. Replace or repair access door so it can opened as designed. Gaps, doesn't cover completely Large access doors not flat and/or access opening not completely covered. Doors close flat; covers access opening completely. Lifting rings missing, rusted Lifting rings not capable of lifting weight of door or plate. Lifting rings sufficient to lift or remove door or plate. Infiltration Pond, Tank, Vault, Trench, or Small Basin Filter Bags Plugged filter bag (if applicable) Filter bag more than 1/2 full. Replace filter bag or redesign system. Infiltration Pond, Tank, Vault, Trench, or Small Basin Pre-settling Ponds and Vaults Sediment accumulation 6" or more of sediment has accumulated. Pre-settling occurs as designed Infiltration Pond, Rock Filter Plugged rock filter High water level on upstream side of filter remains for extended period of time or little or no water flows through filter during heavy rain storms. Rock filter replaced evaluate need for filter and remove if not necessary. Infiltration Pond Emergency Overflow Spillway Rock missing Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil at the top of out flow path of spillway. Rip-rap on inside slopes need not be replaced. Spillway restored to design standards. Tree growth Tree growth impedes flow or threatens stability of spillway. Trees removed. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-10 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Structure Sediment accumulation Sediment exceeds 60% of the depth from the bottom of the catch basin to the invert of the lowest pipe into or out of the catch basin or is within 6 inches of the invert of the lowest pipe into or out of the catch basin. Sump of catch basin contains no sediment. Trash and debris Trash or debris of more than ½ cubic foot which is located immediately in front of the catch basin opening or is blocking capacity of the catch basin by more than 10%. No Trash or debris blocking or potentially blocking entrance to catch basin. Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. No trash or debris in the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within catch basin. Deposits of garbage exceeding 1 cubic foot in volume. No condition present which would attract or support the breeding of insects or rodents. Damage to frame and/or top slab Corner of frame extends more than ¾ inch past curb face into the street (If applicable). Frame is even with curb. Top slab has holes larger than 2 square inches or cracks wider than ¼ inch. Top slab is free of holes and cracks. Frame not sitting flush on top slab, i.e., separation of more than ¾ inch of the frame from the top slab. Frame is sitting flush on top slab. Cracks in walls or bottom Cracks wider than ½ inch and longer than 3 feet, any evidence of soil particles entering catch basin through cracks, or maintenance person judges that catch basin is unsound. Catch basin is sealed and is structurally sound. Cracks wider than ½ inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. No cracks more than 1/4 inch wide at the joint of inlet/outlet pipe. Settlement/ misalignment Catch basin has settled more than 1 inch or has rotated more than 2 inches out of alignment. Basin replaced or repaired to design standards. Damaged pipe joints Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering the catch basin at the joint of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of inlet/outlet pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Inlet/Outlet Pipe Sediment accumulation Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment. Trash and debris Trash and debris accumulated in inlet/outlet pipes (includes floatables and non-floatables). No trash or debris in pipes. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-11 NO. 5 – CATCH BASINS AND MANHOLES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITION WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Inlet/Outlet Pipe (cont.) Damaged inlet/outlet pipe Cracks wider than ½-inch at the joint of the inlet/outlet pipes or any evidence of soil entering at the joints of the inlet/outlet pipes. No cracks more than ¼-inch wide at the joint of the inlet/outlet pipe. Metal Grates (Catch Basins) Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and debris Trash and debris that is blocking more than 20% of grate surface. Grate free of trash and debris. footnote to guidelines for disposal Damaged or missing grate Grate missing or broken member(s) of the grate. Any open structure requires urgent maintenance. Grate is in place and meets design standards. Manhole Cover/Lid Cover/lid not in place Cover/lid is missing or only partially in place. Any open structure requires urgent maintenance. Cover/lid protects opening to structure. Locking mechanism not working Mechanism cannot be opened by one maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not work. Mechanism opens with proper tools. Cover/lid difficult to remove One maintenance person cannot remove cover/lid after applying 80 lbs. of lift. Cover/lid can be removed and reinstalled by one maintenance person. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 12/12/2016 2017 City of Renton Surface Water Design Manual A-12 NO. 6 – CONVEYANCE PIPES AND DITCHES MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Pipes Sediment & debris accumulation Accumulated sediment or debris that exceeds 20% of the diameter of the pipe. Water flows freely through pipes. Vegetation/root growth in pipe Vegetation/roots that reduce free movement of water through pipes. Water flows freely through pipes. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective coating or corrosion Protective coating is damaged; rust or corrosion is weakening the structural integrity of any part of pipe. Pipe repaired or replaced. Damaged pipes Any dent that decreases the cross section area of pipe by more than 20% or is determined to have weakened structural integrity of the pipe. Pipe repaired or replaced. Ditches Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 square feet of ditch and slopes. Trash and debris cleared from ditches. Sediment accumulation Accumulated sediment that exceeds 20% of the design depth. Ditch cleaned/flushed of all sediment and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may constitute a hazard to City personnel or the public. Noxious and nuisance vegetation removed according to applicable regulations. No danger of noxious vegetation where City personnel or the public might normally be. Contaminants and pollution Any evidence of contaminants or pollution such as oil, gasoline, concrete slurries or paint. Materials removed and disposed of according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Excessive vegetation growth Vegetation that reduces free movement of water through ditches. Water flows freely through ditches. Erosion damage to slopes Any erosion observed on a ditch slope. Slopes are not eroding. Rock lining out of place or missing (If applicable) One layer or less of rock exists above native soil area 5 square feet or more, any exposed native soil. Replace rocks to design standards. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-41 NO. 30 – PERMEABLE PAVEMENT BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Preventive Surface cleaning/ vegetation control Media surface vacuumed or pressure washed annually, vegetation controlled to design maximum. Weed growth suggesting sediment accumulation. No dirt, sediment, or debris clogging porous media, or vegetation limiting infiltration. Porous Concrete, Porous Asphaltic Concrete, and Permeable Pavers Trash and debris Trash and debris on the pavement interfering with infiltration; leaf drop in fall season. No trash or debris interfering with infiltration. Sediment accumulation Sediment accumulation on the pavement interfering with infiltration; runoff from adjacent areas depositing sediment/debris on pavement. Pavement infiltrates as designed; adjacent areas stabilized. Insufficient infiltration rate Pavement does not infiltrate at a rate of 10 inches per hour. Pavement infiltrates at a rate greater than 10 inches per hour. Excessive ponding Standing water for a long period of time on the surface of the pavement. Standing water infiltrates at the desired rate. Broken or cracked pavement Pavement is broken or cracked. No broken pavement or cracks on the surface of the pavement. Settlement Uneven pavement surface indicating settlement of the subsurface layer. Pavement surface is uniformly level. Moss growth Moss growing on pavement interfering with infiltration. No moss interferes with infiltration. Inflow restricted Inflow to the pavement is diverted, restricted, or depositing sediment and debris on the pavement. Inflow to pavement is unobstructed and not bringing sediment or debris to the pavement. Underdrain not freely flowing Underdrain is not flowing when pavement has been infiltrating water. Underdrain flows freely when water is present. Overflow not controlling excess water Overflow not controlling excess water to desired location; native soil is exposed or other signs of erosion damage are present. Overflow permits excess water to leave the site at the desired location; Overflow is stabilized and appropriately armored. Permeable Pavers Broken or missing pavers Broken or missing paving blocks on surface of pavement. No missing or broken paving blocks interfering with infiltration. Uneven surface Uneven surface due to settlement or scour of fill in the interstices of the paving blocks. Pavement surface is uniformly level. Compaction Poor infiltration due to soil compaction between paving blocks. No soil compaction in the interstices of the paver blocks limiting infiltration. Poor vegetation growth (if applicable) Grass in the interstices of the paving blocks is dead. Healthy grass is growing in the interstices of the paver blocks. APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS 2017 City of Renton Surface Water Design Manual 12/12/2016 A-47 NO. 38 – SOIL AMENDMENT BMP MAINTENANCE COMPONENT DEFECT OR PROBLEM CONDITIONS WHEN MAINTENANCE IS NEEDED RESULTS EXPECTED WHEN MAINTENANCE IS PERFORMED Soil Media Unhealthy vegetation Vegetation not fully covering ground surface or vegetation health is poor. Yellowing: possible Nitrogen (N) deficiency. Poor growth: possible Phosphorous (P) deficiency. Poor flowering, spotting or curled leaves, or weak roots or stems: possible Potassium (K) deficiency. Plants are healthy and appropriate for site conditions Inadequate soil nutrients and structure In the fall, return leaf fall and shredded woody materials from the landscape to the site when possible Soil providing plant nutrients and structure Excessive vegetation growth Grass becomes excessively tall (greater than 10 inches); nuisance weeds and other vegetation start to take over. Healthy turf- “grasscycle” (mulch-mow or leave the clippings) to build turf health Weeds Preventive maintenance Avoid use of pesticides (bug and weed killers), like “weed & feed,” which damage the soil Fertilizer needed Where fertilization is needed (mainly turf and annual flower beds), a moderate fertilization program should be used which relies on compost, natural fertilizers or slow-release synthetic balanced fertilizers Integrated Pest Management (IPM) protocols for fertilization followed Bare spots Bare spots on soil No bare spots, area covered with vegetation or mulch mixed into the underlying soil. Compaction Poor infiltration due to soil compaction • To remediate compaction, aerate soil, till to at least 8-inch depth, or further amend soil with compost and re-till • If areas are turf, aerate compacted areas and top dress them with 1/4 to 1/2 inch of compost to renovate them • If drainage is still slow, consider investigating alternative causes (e.g., high wet season groundwater levels, low permeability soils) • Also consider site use and protection from compacting activities No soil compaction Poor infiltration Soils become waterlogged, do not appear to be infiltrating. Facility infiltrating properly Erosion/Scouring Erosion Areas of potential erosion are visible Causes of erosion (e.g., concentrate flow entering area, channelization of runoff) identified and damaged area stabilized (regrade, rock, vegetation, erosion control matting).For deep channels or cuts (over 3 inches in ponding depth), temporary erosion control measures in place until permanent repairs can be made Grass/Vegetation Unhealthy vegetation Less than 75% of planted vegetation is healthy with a generally good appearance. Healthy vegetation. Unhealthy plants removed/replaced. Appropriate vegetation planted in terms of exposure, soil and soil moisture. Noxious Weeds Noxious weeds Listed noxious vegetation is present (refer to current County noxious weed list). No noxious weeds present. Appendix D Declaration of Covenant Page 1 of ___ Return Address: City Clerk’s Office City of Renton 1055 S Grady Way Renton, WA 98057 DECLARATION OF COVENANT FOR INSPECTION AND MAINTENANCE OF DRAINAGE FACILITIES AND ON-SITE BMPS Grantor: Grantee: City of Renton, a Washington municipal corporation Legal Description: Assessor's Tax Parcel ID#: IN CONSIDERATION of the approved City of Renton (check one of the following) Residential Building Permit Commercial Building Permit Clearing and Grading Permit Civil Construction or Utility Permit for Permit(s)_____________________ (Construction/Building/Utility Permit #) relating to the real property ("Property") described above, the Grantor(s), the owner(s) in fee of that Property, hereby covenants (covenant) with the City of Renton (“City of Renton” or “City”), a municipal corporation of the state of Washington, that he/she (they) will observe, consent to, and abide by the conditions and obligations set forth and described in Paragraphs 1 through 9 below with regard to the Property, and hereby grants (grant) an easement as described in Paragraphs 2 and 3. Grantor(s) hereby grants (grant), covenants (covenant), and agrees (agree) as follows: 1.The Grantor(s) or his/her (their) successors in interest and assigns ("Owners ") shall at their own cost, operate, maintain, and keep in good repair, the Property's drainage facilities constructed as required in the approved construction plans and specifications __________________ (Project Plan #) on file with the City of Renton and submitted to the City of Renton for the review and approval of permit(s) _____________________________ (Construction/Building/Utility Permit #). The Property's drainage facilities are shown and/or listed on Exhibit A – Site Plan. The Property’s drainage facilities shall be maintained in compliance with the operation and maintenance schedule included and attached herein as Exhibit B – Operations and Maintenance. Drainage facilities include pipes, channels, flow control facilities, water quality facilities, on-site best management practices (BMPs) and other engineered structures designed to manage and/or Yvonne Bui 784130-0400 C22000675 R-4215 C22000675 3 4 4 4 LOTS 5 AND 6, BLOCK 5, SMITHERS FIFTH ADDITION TO THE TOWN OF RENTON, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 16 OF PLATS, PAGE 33, RECORDS OF KING COUNTY, WASHINGTON. Page 2 of ___ treat stormwater on the Property. On-site BMPs include dispersion and infiltration devices, bioretention, permeable pavements, rainwater harvesting systems, tree retention credit, reduced impervious surface footprint, vegetated roofs and other measures designed to mimic pre-developed hydrology and minimize stormwater runoff on the Property. 2.City of Renton shall have the right to ingress and egress over those portions of the Property necessary to perform inspections of the stormwater facilities and BMPs and conduct maintenance activities specified in this Declaration of Covenant and in accordance with the Renton Municipal Code. City of Renton shall provide at least thirty (30) days’ written notice to the Owners that entry on the Property is planned for the inspection of drainage facilities. After the thirty (30) days, the Owners shall allow the City of Renton to enter for the sole purpose of inspecting drainage facilities. In lieu of inspection by the City, the Owners may elect to engage a licensed civil engineer registered in the state of Washington who has expertise in drainage to inspect the drainage facilities and provide a written report describing their condition. If the engineer option is chosen, the Owners shall provide written notice to the City of Renton within fifteen (15) days of receiving the City’s notice of inspection. Within thirty (30) days of giving this notice, the Owners, or engineer on behalf of the Owners, shall provide the engineer’s report to the City of Renton. If the report is not provided in a timely manner as specified above, the City of Renton may inspect the drainage facilities without further notice. 3.If City of Renton determines from its inspection, or from an engineer’s report provided in accordance with Paragraph 2, that maintenance, repair, restoration, and/or mitigation work is required to be done to any of the drainage facilities, City of Renton shall notify the Owners of the specific maintenance, repair, restoration, and/or mitigation work (“Work”) required pursuant to the Renton Municipal Code. The City shall also set a reasonable deadline for the Owners to complete the Work, or to provide an engineer’s report that verifies completion of the Work. After the deadline has passed, the Owners shall allow the City access to re-inspect the drainage facilities unless an engineer’s report has been provided verifying completion of the Work. If the Work is not completed within the time frame set by the City, the City may initiate an enforcement action and/or perform the Work and hereby is given access to the Property for such purposes. Written notice will be sent to the Owners stating the City’s intention to perform such Work. This Work will not commence until at least seven (7) days after such notice is mailed. If, within the sole discretion of the City, there exists an imminent or present danger, the seven (7) day notice period will be waived and Work will begin immediately. 4.The Owners shall assume all responsibility for the cost of any Work, or any measures taken by the City to address conditions as described in Paragraph 3. Such responsibility shall include reimbursement to the City within thirty (30) days of the receipt of the invoice for any such Work performed. Overdue payments will require payment of interest at the maximum legal rate allowed by RCW 19.52.020 (currently twelve percent (12%)). If the City initiates legal action to enforce this agreement, the prevailing party in such action is entitled to recover reasonable litigation costs and attorney’s fees. 5.The Owners are required to obtain written approval from City of Renton prior to filling, piping, cutting, or removing vegetation (except in routine landscape maintenance) in open vegetated stormwater facilities (such as swales, channels, ditches, ponds, etc.), or performing any alterations or modifications to the drainage facilities referenced in this Declaration of Covenant. 3 NORTHExhibit A- Flow Control BMP Site Plan Permit Number:Approved By:Date:C22000675 06/08/22 Permit Number:Approved By:Date:C22000675 06/08/22 Exhibit B- Operations and Maintenance Permit Number:Approved By:Date: Exhibit B- Operations and Maintenance C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit B- Operations and Maintenance C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit B- Operations and Maintenance C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit C- Legal Description C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit B- Operations and Maintenance C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit B- Operations and Maintenance C22000675 06/08/22 Permit Number:Approved By:Date: Exhibit C- Legal Description C22000675 06/08/22